An “inference” is an extrapolation
from a state in one state-space to a state in another state-space,
where both state-spaces describe the same set of real objects. The state-space
from which an extrapolation is made is called the “observed” state-space. The state-space to which an
extrapolation is made is called the “unobserved” state-space. With reference to
an inference from a state in the state-space {cloudy, not cloudy} to a
state in the state-space {rain in the
next 24 hours, no rain in the next 24
hours}, {cloudy, not cloudy} is the observed state-space
while {rain in the next 24 hours, no rain in the next 24 hours} is the
unobserved state-space.